The present invention relates to lactone copolymers having suppressed crystallinity which can render them suitable for use, for example, in the manufacture of biodegradable films for trash bags.
Current environmental concerns have generated interest in the use of biodegradable plastics for disposable items such as, for example, trash bags, packaging materials, eating utensils, and the like. A variety of biodegradable polymers have been proposed for such uses. Typical of such polymers include, condensation polymers, such as, for example, polyesters, polyester amides, polymers formed by ring open polymerization, e.g., lactone, lactide and lactam polymerizations, polyhydroxyalkonoates, polylactic acid and naturally occurring polymers, such as, polysaccharides, e.g., cellulosic, starch, and soy derivatives.
As used herein, the term xe2x80x9cbiodegradablexe2x80x9d, as defined in ASTM D-883, is made with reference to degradable polymers in which the degradation results from the action of micro-organisms occurring naturally such as, for example, bacteria, fungi, and algae. The biodegradability may be evidenced, for example, by the production of CO2 and associated reduction in mechanical properties, such as tensile strength and percent elongation at break. Further details are known to those skilled in the art.
Although many polymers such as those described above, are highly effective in terms of their biodegradability, they often suffer from inferior mechanical performance which has hindered their commercial viability. More specifically, when converted to film by blown film extrusion, for example, biodegradable polymers often do not have good machine direction (xe2x80x9cMDxe2x80x9d) Elmendorf Tear Strength as measured by ASTM D-1922, transverse direction (xe2x80x9cTDxe2x80x9d) Tensile Impact as measured by ASTM D-1822, Falling Dart Impact Resistance as measured by ASTM D-1709, MD and TD Secant Modulus as measured by ASTM D-882, and Puncture Resistance as measured by Union Carbide Test Method WC-68-L. On the other hand, when biodegradable polymers are modified to enhance their mechanical properties, their biodegradability often suffers.
As used herein, the terms xe2x80x9ccondensation polymerizationxe2x80x9d and xe2x80x9cpolycondensationxe2x80x9d mean: (i) a polymerization reaction in which two or more molecules are combined with the generation of water, alcohol or other simple substances as by-products; and (ii) polymerization of monomers, e.g., ester and amide monomers, formed by ring opening polymerization, e.g., lactones, lactides and lactams, which do not generate water, alcohol or other simple substances as by-products.
Often, condensation polymers suitable for use as biodegradable materials are semi-crystalline in form, e.g., greater than about 30%, often greater than about 50% and more often greater than about 70% crystalline. Complete crystallization of polymers is often a slow process requiring minutes, hours or days to fully accomplish. When crystallization is desired, the temperature is held above the glass transition temperature (xe2x80x9cTgxe2x80x9d) and below the crystalline melting point for a time sufficient to allow the molecules of the polymer to order themselves into crystal lattices. This process is also referred to in the art as xe2x80x9cannealingxe2x80x9d. If the crystallinity of the polymer becomes too high, the molded article from the polymer may not have sufficient toughness to be viable in a typical end use like trash bags, mulch film, molded parts and the like.
Accordingly, improved condensation polymers, e.g., lactone polymers, having enhanced mechanical properties are desired which can retain their biodegradable characteristics.
By the present invention, improved lactone polymers are provided. The improvement of the present invention is directed to the use of comonomers in the lactone polymerization which are effective to suppress the crystallinity of the copolymers. Without being bound to any particular theory, it is believed that the suppression of crystallinity can cause enhancements in the mechanical properties of films made from the copolymers compared to copolymers made without the crystallinity-suppressing monomers.
In accordance with the present invention, the suppression of crystallinity may be evidenced by one or more factors. For instance, the suppression of crystallinity may be evidenced by a reduction in the crystallization temperature of the copolymer, or by a reduction in the rate of crystallization of the copolymer, or by a reduction in the melt temperature of the polymer or by a reduction in the crystallinity of the copolymer. As used herein, the term xe2x80x9ccrystallization temperaturexe2x80x9d means the temperature at which formation of the crystalline phase occurs; the term xe2x80x9ccrystallization ratexe2x80x9d means the rate at which formation of the crystalline phase occurs; the term xe2x80x9cmelt temperaturexe2x80x9d means the freezing point and the term xe2x80x9ccrystallinityxe2x80x9d means the degree of crystallinity of the polymer. The crystallization properties of polymers can be readily determined by those skilled in the art, such as, for example, by differential scanning calorimetry (xe2x80x9cDSCxe2x80x9d).
The first monomer suitable for use in accordance with the present invention is a lactone monomer. The first monomer can be ethylenically unsaturated or alternatively can have no ethylenic unsaturation. The molecular structure of the first monomer is not critical for the present invention and can have straight, e.g., normal, alkyl or branched, cyclic or aromatic substituents. In addition, the first monomer can have functional groups selected from the group consisting of esters, ethers, alcohols, acids, amines, amides, acid halides, isocyanates and mixtures thereof as may be determined by those skilled in the art. In addition, the first monomer can be comprised of a single molecular unit, an oligomer or a prepolymer and can have a molecular weight of typically from about 72 to 12,000 grams per gram mole (xe2x80x9cg/gmolxe2x80x9d), more typically, from about 72 to 10,000 g/gmol.
Unless otherwise indicated, as used herein, the term xe2x80x9cmolecular weightxe2x80x9d means number average molecular weight. Techniques for determining number average molecular weight are known to those skilled in the art. One such technique is gel permeation chromatography (xe2x80x9cGPCxe2x80x9d).
In one aspect of the present invention, the lactone monomers include those having the formulas: 
where X=nil, xe2x80x94Oxe2x80x94, or xe2x80x94Oxe2x80x94C=O; Z=1-3; Y=1-4; R1-R4=Hxe2x80x94, xe2x80x94CH3, C2-C16 alkyl group, xe2x80x94C(CH3), or HOCH2xe2x88x92, and where all R""s are independent on each y or z carbon unit and independent of each other; or 
where R1-R4=Hxe2x80x94, xe2x80x94CH3, C2-C16 alkyl group, or HOCH2xe2x80x94, and where all R""s are independent of each other.
Examples of the lactones described above are, but not limited to, caprolactone, t-butyl caprolactone, zeta-enantholactone, deltavalerolactones, the monoalkyl-delta-valerolactones, e.g. the monomethyl-, monoethyl-, monohexyl-deltavalerolactones, and the like; the nonalkyl, dialkyl, and trialkyl-epsilon-caprolactones, e.g. the monomethyl-, monoethyl-, monohexyl-, dimethyl-, di-n-propyl-, di-n-hexyl-, trimethyl-, triethyl-, tri-n-epsilon-caprolactones, 5-nonyl-oxepan-2-one, 4,4,6- or 4,6,6-trimethyl-oxepan-2-one, 5-hydroxymethyl-oxepan-2-one, and the like; beta-lactones, e.g., beta-propiolactone, beta-butyrolactone gamma-lactones, e.g., gammabutyrolactone or pivalolactone, dilactones, e.g. lactide, dilactides, glycolides, e.g., tetramethyl glycolides, and the like, ketodioxanones, e.g. 1,4-dioxan-2-one, 1,5-dioxepan-2-one, and the like. The lactones can consist of the optically pure isomers or two or more optically different isomers or can consist of mixtures of isomers.
xcex5-caprolactone and its derivatives and other seven membered ring lactones are especially preferred for use as first monomers in accordance with the present invention.
In one aspect of the present invention, other monomers may be polymerized with the lactones to comprise the first monomer, such as, for example, one or more compounds which can be polymerized or copolymerized to form aliphatic polyesters or polyester amides or other condensation polymers. Examples of such polymers include, for example, polyesters prepared from the reaction of C2-C6 diols, e.g., ethylene glycol, diethylene glycol, butanediol, neopentyl glycol, hexanediol with dicarboxylic acids, such as but not limited to, succinic, glutaric or adipic acid; copolyesters of terephthalic acid based polymers with dicarboxylic acids and diols; and polyester/amides from the reaction of caprolactam with dicarboxylic acids and diols. Suitable hydroxy acids include, for example, xcex1-hydroxybutyric acid, xcex1-hydroxyisobutyric acid, xcex1-hydroxyvaleric acid, xcex1-hydroxyisovaleric acid, xcex1-hydroxycaproic acid, xcex1-hydroxyisocaproic acid, xcex1-hydroxy-xcex1-ethylbutyric acid, xcex1-hydroxy-xcex2-methylvaleric acid, xcex1-hydroxyheptanoic acid, xcex1-hydroxyoctanoic acid, xcex1-hydroxydecanoic acid, xcex1-hydroxymyristic acid and xcex1-hydroxystearic acid or their intermolecular cyclic esters or combinations thereof. In another aspect of the present invention, the first monomer can additionally comprises cyclic monomers which are polymerized by ring opening polymerization in addition to the lactones. Typical of such monomers are cyclic esters, such as, for example, lactides, glycolides, and cyclic carbonates.
Examples of typical cyclic ester polymers and their (co)polymers resulting from the polymerization of the above-mentioned monomers include: poly(epsilon-caprolactone); poly(L-lactide-co-epsilon- caprolactone); poly(D,L-lactide-co-epsilon-caprolactone); poly(meso-lactide-co-epsilon-caprolactone); poly(glycolide-co-epsilon-caprolactone).
Typically, the amount of the first monomer used in the copolymers of the present invention is from about 50 to 99 wt. %, preferably from about 60 to 98 wt. % and more preferably from about 85 to 95 wt. %, based on the total weight of the monomers in the copolymer. Monomers suitable for use as the first monomer in the copolymers of the present invention are commercially available.
The second monomer suitable for use in preparing the copolymers of the present invention includes any amorphous monomers which are functional to suppress the crystallinity of the copolymer. As used herein, the term xe2x80x9camorphousxe2x80x9d means that the monomer is predominantly amorphous, i.e., greater than 50% amorphous, preferably greater than 70% amorphous and more preferably greater than 90% amorphous, as determined, for example, by DSC measuring the enthalpy of fusion. The second monomer can be ethylenically unsaturated or alternatively can have no ethylenic unsaturation. The molecular structure of the second monomer is not critical for the present invention and can be straight, e.g., normal, alkyl or branched, cyclic or aromatic. In a preferred aspect of the invention, the second monomer is a branched ester. Preferably, the second monomer has a functional group selected from the group consisting of esters, ethers, alcohols, acids, amides, acid halides and mixtures thereof. In addition, the second monomer can be comprised of a single molecular unit, an oligomer or a prepolymer and can have a molecular weight of typically from about 62 to 12,000 g/gmol, more typically, from about 62 to 10,000 g/gmol. Additionally, the second monomer can comprise a derivative of the first monomer, e.g, a branched caprolactone such as, for example, t-butyl caprolactone.
Often, the second monomer is used as an initiator in the polymerization of the first monomer, e.g., to initiate ring opening of cyclic lactone monomers. Typically, the suppression in crystallinity afforded by the second monomer will be evidenced by one or more of the following factors: (i) a reduction in the crystallization temperature of the copolymer of at least 2xc2x0 C., preferably at least 4xc2x0 C. and more preferably at least 6xc2x0 C., as compared to a homopolymer of the first monomer or a copolymer of the first monomer and another monomer which is not effective to suppress the crystallinity, or (ii) a reduction in the crystallinity of the copolymer. Typically, in accordance with the present invention, the crystallinity will be reduced by at least 2 percent, preferably at least 6 percent and more preferably at least 8 percent compared to the crystallinity of a homopolymer of the first monomer or a copolymer of the first monomer and another monomer which is not effective to suppress the crystallinity. The crystallinity can be determined by DSC, measuring the enthalpy of fusion.
In one aspect of the present invention, the second monomer is effective to create amorphous regions in the copolymer. For example if the second monomer is a branched version of the first monomer, it generally will not co-crystallize with the first monomer, thus it will disrupt the crystallization of the first monomer, increasing the amorphous region, decreasing the crystallinity of the copolymer. If the second xe2x80x98monomerxe2x80x99 is a non-crystallizable oligomer, the net crystallinity of the copolymer will be reduced to a level that can enhance molded polymer toughness.
In another aspect of the present invention, the second monomer is effective to introduce branching into the polymer, i.e., pendant chains off the backbone of the copolymer. Preferably, the branching is introduced as short chains into the copolymer backbone. As used herein, the term xe2x80x9cshort chain branchingxe2x80x9d means hydrocarbon branches, e.g., alkyl groups in the polymer backbone, which are preferably, C1 to C16 alkyl groups, which terminate in an unreacted free end, e.g., methyl, propyl, t-butyl. Short chain branching can be introduced into the polymer backbone, for example, by using branched difunctional initiators obtained by polymerizing a linear or branched dicarboxylic acid with a linear or branched diol initiator, such that at least either the acid or diol is branched.
Suitable dicarboxylic acids are of the formula: 
where Y=O to 12; R1 and R2=Hxe2x80x94, xe2x80x94CH3 or C2-Cl16 alkyl group, and where all R""s are independent of each other and each carbon unit. Illustrative of the dicarboxylic acids are succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, and 2-ethyl-2-methylsuccinic acid. In addition to the aliphatic dicarboxylic acids described above, aromatic dicarboxylic acids, such as but not limited to phthalic acid, isophthalic acid, and terephthalic acid can be used.
Suitable diol initiators are of the formula: 
where X=nil, xe2x80x94Oxe2x80x94; a=1 to 6; b=0 to 10; c=nil, C1-C16; and R1-R4=H-, -CH3 or C2-C16 alkyl group, and where all R""s are independent of each other and each carbon unit. Examples of diols are, but not limited to, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,10-decanediol, 1,12-dodecanediol, 1,2-decanediol, 1,2-dodecanediol, 1,2-hexadecanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-ethyl- 3-butyl- 1,3-propanediol, 2-ethyl-1,6-hexanediol.
Of these, 2-butyl-2-ethyl-1,3-propane adipate, prepared from the reaction of 2-butyl-2-ethyl-1,3-propanediol (xe2x80x9cBEPDxe2x80x9d) and adipic acid are preferred. Other methods of introducing short chain branching include the reaction of either the branched or long chain 1,2-diol with xcex5-caprolactone monomer and then transesterification with the diester of a dicarboxylic acid, e.g., transesterification of a BEPD initiated caprolactone oligomer with dimethyladipate, or the reaction of a BEPD initiated caprolactone oligomer with adipoyl chloride, or the reaction of a BEPD initiated caprolactone oligomer with a diisocyanate, i.e. HDI or MDI, or reacting branched lactones with unbranched lactones, e.g. copolymer of t-butyl caprolactone and xcex5-caprolactone. As an alternative or in addition to the polymerized branched monomers, branched polymers can be blended into linear polymers of other molecules to provide short chain branching.
The amount of the second monomer suitable for use in preparing the copolymers of the present invention is effective to suppress the crystallinity of the copolymer. Typically, the amount is from about 1 to 50 wt. %, preferably from about 5 to 35 wt. % and more preferably from about 9 to 20 wt. % based on the total weight of the monomers used to make the copolymer. The optimal level of the second monomer will depend of the specific structure of the second monomer and can be determined by those skilled in the art.
One or more monomers from each of the first monomer group or second monomer group may be used in preparing the copolymers of the present invention. In addition, other monomers may also be employed in addition to the first monomer and second monomer. Such other monomers may be introduced for example in order to impart certain desired properties to the copolymer. The particular other monomers are not critical to the present invention but may include for example, monomers such as dialcohols, e.g., ethylene glycol, 1-4-butanediol, 1,3-propanediol, 1,6 hexanediol, diethylene glycol, etc., dicarboxylic acids, e.g., oxalic acid, succinic acid, adipic acid, amino alcohols, e.g., ethanol amine, propanol amine, amino carboxylic acids, e.g., amino caproic acid and the like. In addition, other monomers can be employed which are normally used to make traditionally non-biodegradable polymers, such as, for example, polyethylene (including low density polyethylene, linear low density polyethylene and high density polyethylene), ethylene vinyl acetate copolymers, ethylene acrylic acid copolymers, polyvinyl chlorides, polystyrenes, chlorinated polyethylenes, ethylene propylene copolymers, acrylic acid copolymers, polyvinyl acetals copolymers, polyamines, polyethylene terephthalates, phenolic resins and urethanes.
In addition to other monomers, the copolymers of the present invention may be blended and/or reacted with other polymers to provide desired characteristics. For instance, the copolymers of the present invention may be extruded with other polymers, such as, for example, polysaccharides, e.g., starch, cellulosics, chitans and the like. Further details of such blended polymer compositions are known to those skilled in art. See for example, U.S. Pat. No. 5,095,054 which is directed to thermoplastic polymer compositions comprising destructurized starch and other polymers, U.S. Pat. No. 5,540,929 which is directed to aliphatic polyester grafted polysaccharides.
Typically, the amount of such other monomers when used in the copolymers of the present invention is from about 1 to 90 wt. %.
Typically, when the copolymers of the present invention are blended or reacted with other polymers, the amount of the other polymer is typically from about 0 to 70 wt. % and preferably from about 20 to 60 wt. % and more preferably from about 30 to 40 wt. % based on the total weight of the blended polymer composition.
Another aspect of the present invention is directed to the introduction of long chain branching into the polymer backbone. In this aspect of the invention, long chain branching can be incorporated in the polymer backbone or polymers containing long chain branching can be blended with the copolymers to improve the proccessability. As used herein, the term xe2x80x9clong chain branchingxe2x80x9d means hydrocarbon branches, e.g., alkyl groups in the backbone which terminate in more than two reactive end groups which result in the preparation of nonlinear polymers. Examples of polymers with long chain branching are, but not limited to, polymers of xcex5-caprolactone with multifunctional initiators such as trimethylolpropane, pentaerythritol, dipentaerythritol and other molecules with multiple hydroxyl or other reactive groups.
The improved proccessability of the copolymers of the present invention can be measured, for example, by determining their Relaxation Spectrum Index (RSI) values. As used herein, the terms xe2x80x9cRelaxation Spectrum Indexxe2x80x9dand xe2x80x9cRSIxe2x80x9d mean the breadth of the distribution of melt state molecular relaxations as calculated from dynamic oscillatory shear tests run in a frequency range from 0.1 to 100 1/sec. The RSI is a sensitive indicator of molecular structure, such as long chain branching, that leads to long relaxation time behavior in the melt state. Further details concerning RSI are known to those skilled in the art. See, for example, J. M. Dealy and K. F. Wissbrun, Melt Rheology and Its Role in Plastics Processing, Van Nostrand Reinhold, 1990, pp. 269-297 and S. H. Wasserman, J. Rheology, Vol. 39, pp. 601-625 (1995).
The processes used to prepare the copolymers of the present invention are not critical. The polymer of the present invention can be prepared by bulk polymerization, suspension polymerization, extruder or solution polymerization. The polymerization can be carried out, for example, in the presence of an inert normally-liquid organic vehicle such as, for example, aromatic hydrocarbons, e.g., benzene, toluene, xylene; ethylbenzene and the like; oxygenated organic compounds such as anisole, dimethyl, and diethyl esters of ethylene glycol; normally-liquid hydrocarbons including open chain, cyclic and alkyl-substituted cyclic saturated hydrocarbons such as hexane, heptane, cyclohexane, decahydronapthalene and the like.
The polymerization process can be conducted in a batch, semi-continuous, or continuous manner. The monomers and catalysts can be admixed in any order according to known polymerization techniques. Thus, the catalyst can be added to one comonomeric reactant. Thereafter, the catalyst-containing comonomer can be admixed with another comonomer. In the alternative, comonomeric reactants can be admixed with each other. The catalyst can then be added to the reactant mixture. If desired, the catalyst can be dissolved or suspended in an inert normally-liquid organic vehicle. If desired, the monomeric reactants either as a solution or a suspension in an inert organic vehicle can be added to the catalyst, catalyst solution or catalyst suspension. Still further, the catalyst and comonomeric reactants can be added to a reaction vessel simultaneously. The reaction vessel can be equipped with a conventional heat exchanger and/or mixing device. The reaction vessel can be any equipment normally employed in the art of making polymers. One suitable vessel, for example, is a stainless steel vessel. A plasticizer, if used, or a solvent can be blended into the polymer to aid in removal of the polymer material from the reactor vessel.
Typically, the polymerization reactions are conducted at a temperature of from about 70 to 250xc2x0 C., preferably from about 100 to 220xc2x0 C., over a reaction time of from about 3 minutes to 24 hours preferably from about 5 to 10 hours. The reaction pressure is not critical to the present invention. The particular catalyst used in the polymerization is not critical and can be determined by those skilled in the art. However, one preferred catalyst for the polymerization of caprolactone with BEPD adipate is tin carboxylate. The catalyst and initiator may be combined in the same molecule, e.g., a aluminum alkoxide.
In addition to the monomers, other ingredients may be added, such as plasticzers, e.g. epoxidized soybean oil, epoxidized linseed oil, triethyl citrate, acetyltriethyl citrate, tri-n-butyl citrate, acetyltri-n-butyl citrate, acetyltri-n-hexyl citrate, glycerin, diethylphthalate, dioctylphthalate; slip/antiblocks, e.g. stearamide, behenamide, oleoamide, erucamide, stearyl erucamide, erucyl erucamide, oleyl palmitamide, steryl stearamide, erucyl stearamide, N,Nxe2x80x2-ethylenebisstearamide, N,Nxe2x80x2-ethylenebisoleamide, talc, calcium carbonate, kaolin clays, molecular sieves and other particulate materials, stabilizers, compatabilizers, nucleating agents, pigments, etc. Typically, the total amount of such other ingredients ranges from about 0.01 to 10 weight percent, based on the total weight of the copolymer composition. Further details concerning the selection and amount of such additives are known to those skilled in the art.
The copolymers produced in accordance with the present invention typically have a melting point of from about 50 to 240xc2x0 C., preferably from about 52 to 120xc2x0 C., and a Tg of from about xe2x88x92120 to 120xc2x0 C. and preferably from about xe2x88x9260 to 60xc2x0 C. The copolymers typically have a Melt Flow of from about 0.1 to 7, preferably from about 0.2 to 2.5 and more preferably from about 0.5 to 2. As used herein, the term xe2x80x9cMelt Flowxe2x80x9d means grams of material that flow through a die in ten minutes at 125xc2x0 C./2.16 kilograms (xe2x80x9cKgxe2x80x9d) as described in ASTM D-1238.
The density of the copolymers typically ranges from about 1.00 to 1.50 grams per cubic centimeter (xe2x80x9cg/ccxe2x80x9d) and preferably from about 1.05 to 1.20 g/cc. Preferably, the addition of amorphous blocks or branching (either short and/or long chain) will lower the density of the copolymer relative to the homopolymer in the solid state. Reducing the density can result in improved polymer toughness properties. Preferably, the copolymers of the present invention have a reduction in density of at least 0.004 g/cc and more preferably from about 0.004 to 0.040 g/cc relative to a homopolymer of the first monomer (exclusive of initiator.)
Typically, the copolymers of the present invention have a weight average molecular weight (Mw) of from about 500 to 800,000 grams/gram mole, and preferably from about 50,000 to 500,000 grams/gram mole. Typically, the number average molecular weight (Mn) ranges from about 500 to 700,000 grams/gram mole, preferably from about 30,000 to 500,000 grams/gram mole. The Polydispersity Index (Mw/Mn) typically ranges from about 1.3 to 10.
Upon completion of the polymerization reaction, the copolymers can be recovered by any means known to those skilled in the art. Preferably in accordance with the present invention, the copolymer is transported in its molten state directly to a pelletizer, extruder or molding machine in order to produce the desired product. These products can be produced in any form known to those skilled in art, such as, for example, fibers, pellets, molded articles, films, sheets, and the like.
The copolymer compositions of the present invention can be converted into cast or blown film, sheet, blow molded, injection molded, or spun into fibers using any process or equipment known to those skilled in the art. Typically, the films have a thickness of from about 0.5 to 2 mils, preferably from about 0.6 to 1.7 mils, and more preferably from about 0.7 to 1.5 mils. The mechanical properties recited herein are based on a film thickness of 1.0 to 1.3 mils. Typically, the films have a MD tensile strength of from about 3000 to 9000 psi, preferably from about 4000 to 8000 psi, with an MD elongation at break of about 250 to 900 percent, preferably from about 400 to 800 percent, as measured by ASTM D-882. Typically, the films have a TD tensile strength from about 2000 to 8000 psi, preferably from about 4000 to 6000 psi, with an elongation at break of about 300 to 1000 percent, preferably from about 500 to 900 percent. The dart drop impact properties of the films typically range from about 20 to 200 grams per 1/1000 inch (xe2x80x9cg/milxe2x80x9d), preferably at least 50 g/mil and more preferably range from about 50 to 150 g/mil. The MD elmendorf tear properties of the films typically range from about 5 to 200 g/mil and preferably range from about 15 to 150 g/mil. The TD elmendorf tear properties of the films typically range from 100 to 700 g/mil. The MD secant modulus properties of the films typically range from 30,000 to 100,000 psi and preferably range from about 30,000 to 80,000 psi. The TD secant modulus properties of the films typically range from 30,000 to 130,000 psi and preferably range from about 30,000 to 80,000 psi. The MD tensile impact properties of the films typically range from 400 to 1100 ft-lb/cu in and preferably range from about 400 to 1700 ft-lb/cu. The TD tensile impact properties of the films typically range from 70 to 1100 ft-lb/cu in and preferably range from about 200 to 1700 ft-lb/cu. The puncture resistance properties of the films typically range from 3 to 50 in-lbs/mil and preferably range from about 10 to 50 in-lbs/mil.
The copolymers of the present invention can be used in the fabrication of a wide variety of products including, for example, sheets, i.e., greater than 10 mil thick, films, i.e., less than 10 mil thick, e.g., trash bags, fibers, e.g., sutures, fishing line and non-woven fabrics and molded articles, e.g., containers, tools and medical devices, such as, for example, staples, clips, pins, prostheses, etc. One particularly preferred end use in accordance with the present invention is to provide compostable film for use as a trash bag. As defined in ASTM D-883, a compostable plastic is a plastic that undergoes biological degradation during composting to yield carbon dioxide, water, inorganic compounds, and biomass at a rate consistent with other known compostable materials and leaves no visually distinguishable or toxic residues.
Typically the copolymers of the present invention are substantially biodegradable. More specifically, the copolymer compositions typically are biodegradable and compostable by ASTM D- 5338, which is a standard test method for Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions.